Fix typo in include guard
Fix typo in include guard

Found by krazy.

janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting,janusw/syntax-highlighting